Tunable optical sorting and manipulation of nanoparticles via plasmon excitation.

We numerically investigate the optical forces exerted by an incident light beam on Rayleigh metallic particles over a dielectric substrate. In analogy with atom manipulation, we identify two different trapping regimes depending on whether the illumination is performed within the plasmon band or out of it. By adjusting the incident wavelength, the particles can be selectively guided, or immobilized, at the substrate interface.